We buy grain from the feed mill and it comes in those white plastic bags. Usually I reuse these for garbage bags, but they also make reusable grocery bags. Cut off the top half of a hundred pound sack. Hem the top edge. Cut the top half into handles, hem and attach at the sides of the bag. Give your kids a box of permanent markers and let them decorate your bag. Depending on the amount of grain that you buy, you could have a mess of these. Enough to maybe even sell some as a fund raiser for your homeschool or 4-H club.
It's all part of being a good steward.